The present invention generally relates to devices for measuring dimensions of a body. The invention particularly relates to devices for measuring the profile and/or diameter of a cylindrical body, such as a roll used in the production of sheet products.
Cylindrical rolls used to roll sheet products, such as aluminum and paper, are required to have a particular profile in order to obtain a flat rolled product. For this reason, the contours or profiles of such rolls must be accurately measured and variations in diameters along their lengths recorded. Freestanding saddle-type micrometers have been widely used for this purpose.
As represented in U.S. Pat. No. 5,088,207 to Betsill et al., a freestanding saddle micrometer generally includes a saddle supported on wheels for rolling (“skating”) along the longitudinal length of a roll. As used herein, the term “freestanding” is used in reference to a saddle-type micrometer in that such micrometers are not mounted to a grinder or other permanent apparatus, but instead are portable and placed on the roll being evaluated. The Betsill et al. saddle micrometer is a caliper-type unit, in that the micrometer has oppositely-disposed arms that extend outward and downward from the saddle so as to be located on opposite sides of a roll when the micrometer is placed on top of a roll. The arms are supported by a rocking crossbar. One of the arms supports a counterweight or follower probe, while the second arm carries an indicator probe, such as a dial indicator or an LVDT (linear variable differential transducer). By locating the follower and indicator probes on their respective arms to be diametrically opposite each other relative to the roll, variations in the diameter of the roll can be detected by skating the saddle along the length of the roll. If a dial indicator is used as the indicator probe, the saddle must make stops along the length of the roll to allow manual recording of the dial indicator reading. If an LVDT or other electronic transducer is used, variations in the roll diameter can be continuously recorded electronically. The saddle is preferably equipped with an encoder to measure the distance skated along the length of the roll, and a minicomputer is mounted on the frame to read, record, and present input data from the LVDT and the encoder.
Saddle micrometers of the type described above have shortcomings that involve compromises in weight, rigidity, balance and operation. In terms of weight and rigidity, such saddle micrometers have taken two approaches: either ignore weight for the sake of rigidity, which results in a unit that operators find difficult to handle but will provide accurate readings, or reduce weight to provide a unit that can be more easily handled but sacrifices rigidity to the extent that imprecise readings may occur. This problem is exacerbated if electronic probes are used, since the unit is constantly in motion as readings are taken. Nonetheless, lighter-weight units are typically more widely accepted because of the difficulty in handling heavier, more rigid units. Such saddle micrometers are also generally top heavy, with the result that the units are more prone to slip off the top of a roll. In the event of slipping off a roll, if a heavier unit is used the unit will probably not be damaged but the operator is at risk of injury. On the other hand, if a lightweight unit slides off a roll, the unit is much more likely to be damaged.
From an operational standpoint, caliper-type micrometers of the type described above do not actually measure roll diameter, but instead are limited to determining the profile of a roll, i.e., variations in diameter along the length of a roll. Furthermore, micrometers have relied on an onboard minicomputer to acquire and process the collected data. Many electronic saddle micrometers are a simple unit that is easy to learn and operate, but provides only basic profile information. More advanced units are available that require extensive training to learn and skill to operate. While providing more detailed profile information, roll history and hard copy printout, in practice such enhanced capabilities were rarely used because of the difficulty in learning how to operate the onboard minicomputer.
From the above, it can be seen that saddle micrometers that overcome the above-noted shortcomings are desirable. An example of such a saddle micrometer is disclosed in U.S. Pat. Nos. 6,820,347 and 7,107,696, the contents of which are incorporated herein by reference. In particular, there is an ongoing desire for micrometers that overcome the above-noted shortcoming comprise relatively compact construction to promote safety and ease of use.